Liquid detergent compositions intended for use as dishwashing products conventionally take the form of clear aqueous solutions containing a mixture of one or more sulphate and sulphonate anionic surfactants together with a suds stabilising agent. Recently there has been a trend towards the use of magnesium cations for at least part of the anionic surfactants present, typified by the disclosures of British Patent Specifications Nos. 1,524,441 and 1,551,074, British published Patent Application No. 2,010,893 A and European Patent Application Publication No. 0039110. The art teaches that these formulations have enhanced performance, particularly when used in water of low mineral hardness. Nevertheless, the pressure to improve the cost-effectiveness of liquid detergent compositions has meant that the search has continued for compositions having improved economy, performance and in-use characteristics. In particular, intensive effort has been expended in increasing the concentration of dishwashing liquid detergent compositions and in reducing the level of non-performing ingredients such as solvents and solubilising hydrotropes without sacrificing the storage stability of the compositions.
Ethoxylated nonionic surfactants constitute a class of materials capable of solubilising other components in aqueous media but this capability is strongly dependent on their average degree of ethoxylation (E.sub.av). Highly ethoxylated nonionic surfactants, (i.e. E.sub.av &gt;20), are very hydrophilic in nature and thus tend to reduce the oily soil removal capability of liquid dishwashing detergent formulations, which is undesirable where oil and grease removal is an important criterion of consumer acceptance. On the other hand nonionic surfactants having low levels of ethoxylation (i.e. E.sub.av .ltoreq.2) are relatively hydrophobic and have a limited ability to form homogeneous solutions with other components in the absence of other surfactant species.
A feature shared by all ethoxylated nonionic surfactants is the present of a level of unethoxylated material, the magnitude of which depends on the degree of ethoxylation, but which can constitute up to 20% by weight of the nonionic surfactant. Unethoxylated C.sub.6 -C.sub.13 aliphatic primary alcohols are odorous materials having a low water solubility, and these characteristics are discernible in the ethoxylated alcohols to an extent which depends on the level of ethoxylation, the effect diminishing as E.sub.av increases.
Liquid dishwashing detergent compositions containing alkyl sulfates and/or alkyl benzene sulfonates have been found to be particularly subject to odour and storage stability problems when formulated with ethoxylated nonionic surfactants containing the normal spread of ethoxylated species, and this effect is more pronounced when the composition also contains magnesium ions. However, the Applicants have established that certain alcohol ethoxylates, containing less than a defined amount of unethoxylated species, and from which preferably at least part of the mono-ethoxylated species has been removed, can be incorporated in alkyl benzene sulfonate- or alkyl sulfate-containing liquid dishwashing detergent compositions without adverse effect on the storage stability of the latter. The Applicants' copending European Application No. 84303044.6 publication No. 0125854 relates to liquid dishwashing detergent compositions of this type.
Zwitterionic surfactants are also known components of detergents compositions particularly in combination with other surfactant species. Disclosures of compositions of this type are provided by European Patent Application Publication No. 0036625 and UK Patent Application No. 2103236A, both of which relate to liquid detergent compositions containing mixtures of alkyl ethoxy sulfate sin combination with other anionic surfactants and a surface active betaine. Another disclosure is provided by Thiele et al. U.S. Pat. No. 3,634,266 which describes an amylase-containing liquid detergent composition in which the surfactant system comprises a mixture of alkyl ethoxy sulfate, ethoxylated nonionic and sulfobetaine species.
Nevertheless,it appears that the efficacy of a zwitterionic detergent in providing enhanced grease and particulate soil removal performance is a function not only of the structure of the zwitterionic surfactant itself, but also of the detergent composition into which it is blended. In particular, it has been found that zwitterionic surfactants that give a suds mileage benefit and/or acceptable greasy soil redeposition performance in one detergent matrix do not give a similar benefit over the same range of usage conditions in other matrices.
The Applicants have now made the discovery that certain narrowly defined classes of betaines provide an unexpected improvement in the soil handling capability of the compositions of the general type disclosed in the previously mentioned European Application No. 0125854.
Accordingly in the present invention there is provided a physically stable enzyme-free liquid detergent composition consisting essentially of from about 22% to about 65% by weight of a surfactant system composed of a mixture of anionic, nonionic and zwitterionic surfactants in an organic solubiliser/hydrotrope-water medium wherein
(i) the anionic surfactant comprises in combination PA1 wherein, in said anionic surfactant combination, the cations include magnesium ion in a molar amount corresponding to from about 35% to about 65% of the molar amount of alkyl sulfate present in the combination; PA1 (ii) the nonionic surfactant comprises from about 1% to about 10% by weight of the composition of an ethoxylated C.sub.6 -C.sub.13 aliphatic alcohol containing an average of from about 1.5 to about 25 moles of ethylene oxide per mole of alcohol, said ethoxylated alcohol containing not more than about 1% by weight of unethoxylated alcohol where the alcohol contains an average of less than about 9 moles of ethylene oxide and not more than about 2% by weight of unethoxylated alcohol where the ethoxylated alcohol containing an average of from about 9 to about 25 moles of ethylene oxide per mole of alcohol; PA1 (iii) the zwitterionic surfactant comprises from about 0.25% to about 10% by weight of the composition of a compound of the general formula ##STR1## wherein R.sub.1 is C.sub.10 -C.sub.16 alkyl PA1 R.sub.3 is a --(CH.sub.2).sub.3 group or a ##STR2## Y is ##STR3## n and m are O or 1 X.sup.- is CH.sub.2 COO.sup.- or SO.sub.3.sup.- ;
(a) from about 4% to about 20% by weight of the composition of a primary C.sub.10 -C.sub.16 alkyl sulfate; PA2 (b) from about 5% to about 20% by weight of the composition of a C.sub.10 -C.sub.16 linear alkyl benzene sulfonate; PA2 (c) from about 5% to about 24% by weight of the composition of a C.sub.10 -C.sub.16 alkyl ethoxysulfate containing an average of up to about 6 moles of ethylene oxide per mole of ethoxysulfate; PA2 R.sub.2 is C.sub.1 -C.sub.3 alkyl PA2 R.sub.2 is C.sub.1 -C.sub.3 alkyl PA2 R.sub.3 is a --(CH.sub.2).sub.3 group or a ##STR5## Y is ##STR6## n and m are O or 1 X.sup.- is CH.sub.2 COO.sup.- or SO.sub.3.sup.- ;
provided that where X.sup.- is CH.sub.2 COO.sup.- m is O and where X.sup.- is SO.sub.3.sup.- m is 1.
Preferably, in the zwitterionic surfactant, R.sub.10 is C.sub.10 -C.sub.16 alkyl, R.sub.2 is methyl and n is O and more preferably the zwitterionic surfactant is a C.sub.12 -C.sub.14 alkyl betaine, present in an amount of from about 0.5% to about 5%, most preferably in an amount of from about 1.0% to about 2.5% by weight of the composition.
Preferably the ethoxylated aliphatic alcohol has an HLB in the range from about 8.0 to about 17.0 more preferably from about 11.0 to about 17.0, and more preferably from about 11.0 to about 15.0. Preferred compositions in accordance with the invention contain from about 3 to about 5% of a C.sub.9 -C.sub.11 primary alcohol condensed with an average of about 6 to about 10 moles of ethylene oxide per mole of alcohol. Preferably, the ethoxylated aliphatic alcohol contains less than about 0.7%, most preferably less than about 0.5% of unethoxylated material, and in highly preferred compositions the level of mono-ethoxylated C.sub.9 -C.sub.11 alcohol is no more than about 5% by weight of the nonionic surfactant.
One useful group of compositions incorporates a three component anionic surfactant system, comprising 6-12% by weight of the composition of C.sub.10 -C.sub.16 primary alkyl sulfate, 6-14% of a C.sub.10 -C.sub.16 primary alkyl ethoxysulfate containing an average of from about 1.5 to about 3 ethoxy groups per alkyl group, and from about 5 to about 15% of a C.sub.10 -C.sub.16 alkyl benzene sulfonate. The cations in this system are a mixture of ammonium and magnesium ions, the level of magnesium corresponding to approximately one half of the molar amount of alkyl sulfate present.
Highly preferred compositions in accordance with the invention incorporate an anionic surfactant system containing from about 15 to about 20% by weight of the composition of a primary C.sub.12 -C.sub.14 alkyl ethoxy sulfate stock containing an average of from about 0.8 to about 2.0 ethylene oxide groups per mole of C.sub.12 -C.sub.14 alkyl ethoxy sulfate, this alkyl ethoxy sulfate stock also including from about 6 to about 10%, by weight of the composition, of C.sub.12 -C.sub.14 alkyl sulfate, together with from 5 to 10% by weight of the composition of A C.sub.11.8 linear alkyl benzene sulfonate component.
Preferably compositions in accordance with the invention also contain from about 2% to about 8%, most preferably by 3%-4% by weight of a suds booster selected form C.sub.10 -C.sub.16 alkyl mono-or di-C.sub.2 -C.sub.3 alkanolamide.